A New Modular Tool Set for Live Imaging and Manipulating the Nervous System Project summary. The nervous system contains the most complex and heterogeneous set of cell types in the body. Modern approaches in imaging, and genetically encoded reporters based on the Green Fluorescent Protein (GFP), have made it possible to explore some of the dynamic processes involved in the development, function, and pathogenesis of the nervous system. However, the complexity of the nervous system has made it difficult to precisely target expression to particular sets of neurons. The objective of this proposal is to create and test prototypes of an entirely new generation of genetically encoded, modular fluorescent molecules for labeling and imaging specific cell types and for manipulating the genes that they express. Specific promoters for many cell types of the nervous system are not available, barring genetic access to these cells. Using an innovative combinatorial strategy, this project will provide access to these cells and enable researchers to specifically target gene expression and gain new insight into signal transduction, protein-protein interaction, and the dynamic processes of neuronal function and pathogenesis. Aim one is to create a modular pair of labeling proteins, the Fly and the Hook, that are tied together by leucine zippers. This modular system will provide access to neurons that have eluded labeling and purification to date. Aim two is to create a bi-functional, modular system for both labeling neurons and manipulating their genomes with complementing proteins that produce both fluorescence and Cre recombinase activity. A New Modular Tool Set for Live Imaging and Manipulating the Nervous System Project Narrative The development and function of the nervous system, as well as the death of neurons in disease and injury, are dynamic processes that are poorly understood. The goal of this project is to develop new fluorescent molecules for genetically labeling and manipulating gene expression in specific neurons in the living brain. If this project is feasible, these molecules would lead to new understanding of the dynamic processes that underlie the pathogenesis of neurological diseases such as epilepsy, stroke and Alzheimer's.